According to the background of the invention, card readers for cards equipped with memory are well known so that we do not need to go into more detail here in this context. However, to better understand the invention we state that all known card readers have a slot equipped with an insertion aperture in which the card equipped with memory is inserted. As such cards are used to produce and/or maintain operating states of electrical devices, there are contacts within the slot that, when the card is inserted in the slot, make contact with the contacts on the card and consequently connect the memory of the card with a read and/or write device. This allows the corresponding device to only be used when there is information stored in the memory of the card. Such cards equipped with memory could be, for example, the SIM cards used in mobile communication, without which the user cannot log into the network. Such cards equipped with memory are often designed so that not only data used to produce and/or maintain operating states is stored in the storage space of the memory, but so that there are also memory areas in which the user himself can write data. In this context we would like to refer again to the SIM cards used in mobile telephones that not only contain the data used to maintain the operating state of mobile telephones, but that also can store telephone numbers entered by the user, for example. This is especially practical because the user, when using another mobile telephone, also has the telephone book stored in the memory of his SIM card available when “his” SIM card is inserted. However, due to the standardization of the memory in the cards, the memory space provided for use by a user is very limited. The memory bottleneck created by the standardization is especially critical because more services and/or applications are constantly being created that need the memory space provided on the cards so that they can be used more flexibly. This need can be met, for example, by providing at least one other card equipped with memory for this purpose that, to increase flexibility, does not necessarily have to be identical to the standard card used in the corresponding application. However, due to the fact that this other card must function with the card already present, it is the task of the invention to specify a method and/or a card reader that prevents invalid states from arising when two cards are used.